Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.42   12.734%   $66.9865   $66.99   $67.00   $67.00  
  Purchase #2 $234.82   12.857%   $265.0108   $265.01   $265.00   $265.00  
  Purchase #3 $184.79   8.202%   $199.9465   $199.95   $199.95   $199.90  
  Purchase #4 $43.55   13.106%   $49.2577   $49.26   $49.25   $49.30  
  Purchase #5 $184.56   5.795%   $195.2553   $195.26   $195.25   $195.30  
  Purchase #6 $113.95   5.364%   $120.0623   $120.06   $120.05   $120.10  
  Purchase #7 $133.35   3.756%   $138.3586   $138.36   $138.35   $138.40  
  7 purchase totals = $954.44       $1,034.8777   $1,034.89   $1,034.85   $1,035.00